Avalanche forecast

Northwest Coastal

Dec 24 – 25, 2011Avalanche Canada
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Avalanche danger

Mon
Tue
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–4
    Strong southwest winds have created windslabs on lee and cross-loaded terrain in the alpine and at treeline. Rider triggered wind slabs are very likely.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–5
    Were the deeply buried mid-December crust/facet layer persists, there is a possibility of highly destructive avalanches. This layer may simply be waiting for the right trigger (cornice fall, trenching sled track)

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Storm slabs will continue to develop on all aspects with forecast weather. Fluctuating freezing levels (especially in the south) will determine the presence of storm slabs below treeline.

Confidence

Fair - Intensity of incoming weather is uncertainfor the entire period

Weather Forecast

Sunday: 5cm of snow - Freezing level at 500m - moderate westerly windsMonday: 20-30cm of snow - Freezing level at 400m - strong southwest windsTuesday: light to moderate snowfall - Freezing level at or around surface - light southwest winds

Avalanche Summary

On the 23rd a natural avalanche cycle took place in the northern part of the region producing slides up to size 3. In the south, observations were extremely limited due to poor visibility. Expect widespread natural avalanche activity throughout the forecast period with expected snow and wind.

Snowpack Summary

Over the past week the forecast region got slammed by snow, strong to extreme wind and fluctuating freezing levels. Including the 18cm that fell on friday night, the southern part of the region has received about 120cm of new snow (Kasiks, Terrace areas). Locations to the north are seeing less (Stewart up to 75cms). Alpine observations have been limited and wind sensors have been disabled by rime, but I suspect new snow has been blown around by strong southwest winds creating wind slabs on lee slopes.In addition to the more obvious direct-action storm instabilities that are expected with the forecast weather, local avalanche professionals have some other concerns: Surface hoar that formed during the winter solstice sits approximately 35cm below the surface and will become more reactive with more wind and snow. As well, the crust-facet combo (extends up to alpine elevations in the south and to 1000m in the north) from the early december dry-spell sits about 150cm below the surface and has not gone away. Any avalanches on this layer would be highly destructive and are probably waiting for the right load or trigger. The mid and lower snowpack are settled out and strong. Snowpack depths in the Kasiks, Terrace areas have reached the 300cm mark. Further north Smithers, Bear Pass depths are ranging from 190-260cms.

Regions covered